This invention relates to a light-sensitive litho printing plate, more particularly to a light-sensitive litho printing plate which can give a printing plate requiring no dampening water with a sharp image after developing, and further will not contaminate hands or clothings after developing, etc.
In the prior art, as the light-sensitive litho printing plate (hereinafter called "plate material" if necessary) requiring no dampening water, one having a light-sensitive layer and an ink repellent layer provided successively by coating on a support has been known. By subjecting the plate material to exposure and developing, a litho printing plate (hereinafter called "printing plate" if necessary) can be obtained.
Such plate materials include those which dissolve the unexposed portion (image portion) of the light-sensitive material by use of a developer and remove the silicone rubber layer of the upper layer accompanied therewith as described in Japanese Patent Publication No. 22781/1980, and those which adhere the exposed portion (non-image portion) firmly to the light-sensitive layer by photoadhesion and remove only the silicon rubber layer at the unexposed portion (image portion) by swelling it with an organic solvent as disclosed in Japanese Unexamined Patent Publication No. 26923/1979.
Among them, those of the type which remove only the silicone rubber at the unexposed portion (image portion) by swelling it with an organic solvent involve the problem that, when the image is observed after developing, it can be seen very difficultly, because only the silicone rubber layer is removed by developing.
Those which have solved this problem are disclosed in, for example, Japanese Unexamined Patent Publications Nos. 103103/1979, 133153/1988, etc., in which it is specifically disclosed to dye the light-sensitive layer or the primer layer exposed after developing with a dye, but these involve the undesirable problems on account of use of a dying solution such that the hands or clothings are contaminated with a dyeing solution remaining on the printing plate surface, or that the automatic developing machine is contaminated with a dyeing solution.
Accordingly, the present inventors have continued intensively studies in order to improve the above-mentioned problems, and consequently found that not only a printing plate with a sharp image can be obtained, but also hands or clothings will not be contaminated with a dyeing solution, or the automatic developing machine will not be contaminated, by incorporating a substance which forms color through the reaction with a component in the processing solution into the light-sensitive layer, to accomplish the present invention.
Therefore, an object of the present invention is to provide a light-sensitive litho printing plate requiring no dampening water which can give a printing plate requiring no dampening water with a sharp image after developing, and further will not contaminate hands or clothings, or contaminate an automatic developing machine with a dyeing solution after developing, etc.